Lewis Base Activation of Lewis Acids: Catalytic, Enantioselective Addition of Silyl Ketene Acetals to Aldehydes
作者:Scott E. Denmark、Gregory L. Beutner、Thomas Wynn、Martin D. Eastgate
DOI:10.1021/ja047339w
日期:2005.3.1
The concept of Lewisbase activation of Lewisacids has been reduced to practice for catalysis of the aldolreaction of silyl ketene acetals and silyl dienol ethers with aldehydes. The weakly acidic species, silicon tetrachloride (SiCl4), can be activated by binding of a strongly Lewis basic chiral phosphoramide, leading to in situ formation of a chiral Lewisacid. This species has proven to be a competent
Lewis Base Activation of Lewis Acids. Addition of Silyl Ketene Acetals to Aldehydes
作者:Scott E. Denmark、Thomas Wynn、Gregory L. Beutner
DOI:10.1021/ja0282947
日期:2002.11.1
olefinic aldehydes as well as aliphatic aldehydes (albeit more slowly) with excellent enantioselectivity. The homologous tert-butyldimethylsilyl ketene acetal of tert-butyl propanoate adds with nearly exclusive anti diastereoselectivity to a similar range of aldehydes also with excellent enantioselectivity. The origin of the slower reaction rate with aliphatic aldehydes is revealed to be the formation of chlorosilyl
Conjugate reduction of aryl acrylates with tributyltin hydride in the presence of magnesium bromide diethyl etherate
作者:Satomi Hirasawa、Hajime Nagano、Yoko Kameda
DOI:10.1016/j.tetlet.2004.01.028
日期:2004.3
The conjugate reduction of aryl acrylates performed with tributyltinhydride in the presence of magnesium bromide diethyl etherate in dichloromethane gave the corresponding saturated esters in moderate to high yields. The reduction of α-methylene-γ-benzyloxycarboxylic acid esters proceeded syn-selectively, but α-methylene-β-oxycarboxylic acid esters afforded reductive elimination products under the
The catalytic asymmetric aldol reaction of aldehydes with unsubstituted and monosubstituted silyl ketene acetals: formation of anti-β-hydroxy-α-methyl esters
作者:Emma R. Parmee、Yaping Hong、Orin Tempkin、Satoru Masamune
DOI:10.1016/s0040-4039(00)91717-9
日期:1992.3
The title reaction with unsubstituted and monosubstituted silyl ketene acetals proceeds with high enantioselectivity, and in the latter case good diastereoselectivity favoring the anti-β-hydroxy-α-methyl esters in all reported cases.
Asymmetric aldol reactions of ketenesilylacetals with aldehydes using an air-stable, storable chiral zirconium catalyst, which could be stored for at least 13 weeks at room temperature, proceeded smoothly to afford the desired adducts in high yields with high selectivity.